Re: a union is always a join!

"Walter Mitty" <wamitty_at_verizon.net> wrote in message news:iVsvl.538$SU3.68_at_nwrddc02.gnilink.net...
>
> "Brian Selzer" <brian_at_selzer-software.com> wrote in message
> news:pi_rl.24249$ZP4.5099_at_nlpi067.nbdc.sbc.com...
>
>> My point has little if anything at all to do with transactions and
>> concurrency control. Those belong to implementations. My point is that
>> relational calculus, or any equivalent mechanism such as relational
>> algebra, while necessary for describing database updates, is not
>> sufficient for that purpose because it can only apply to a single
>> database, not two successive databases. The mechanism of updating the
>> database cannot be reduced to mere algebraic expressions, but instead to
>> asserting, in the context of what has been the case, just what in the
>> world is different and exactly how. Let me explain.
>
> I finally figured out that this is where the discussion branched off into
> what some of us consider mysticism.
>
> I disagree with the last sentence. In particular, the phrase "just what
> in
> the world is different" implies, if I read it correctly, that a database
> update has to be mapped into a "real world update".

I don't agree with that characterization. A world is just a snapshot of the universe of discourse. The universe of discourse is only an abstraction of at most a subset of reality--if that--and is limited to just what is interesting, so the context of "just what in the world is different" is definitely not "the real world."

<snipped the remainder of your argument because it is based on a false premise> Received on Tue Mar 17 2009 - 00:50:00 CET